You could - THEORETICALLY, but not practically !!! I was trying to do the same, like you asked ... and a realised, that you would have to power up each coil differently in a order and then make it faster, so your rotor turns faster - that's almost impossible without the chip.

To understand that, try to put power in one coil - hold - and the rotor will probably move and stop in a fixed position related to the coil. And then, if you powered up a different coil - just by touching it (not holding) you would give an impulse for the rotor to turn. But if you held it, it would just move a bit and stayed still in the fixed position to the coil you are powering it up.

The extra circuit doesn't have to be complicated but it does have to be able to sequence the coils in the correct order and a the proper frequency for the speed you want it to run. And it has to be able to carry the current the motor takes. A regular disk drive won't use much current so that should not be too hard to accomplish.

SOLUTION!!! Its actually IS theoretically possible, heres a video of me doing it, though its very crude and cant be used in a big project, it doesn't work very well, but it works: http://www.youtube.com/watch?v=CWx5ji_sFUw

1. You can use the original PCB that comes on the hard drive to power the motor. You will have to run a couple of wires to ground on some hard drive to trick the PCB in keeping the motor running. Some hard drive PCB's will allow the motor to spin continually and some will stop after a certain amount of time.

2. You can build a DIY BLDC drive circuit using nothing but a handful of transistors and a signal generator. Some have even done it with a handful of transistors and a 555 timer. There are more stable options but they are more involved.

3. You can rewire the motor with larger gauge wire and attach blades to it and use it as a generator. There are many tutorials on the net with step by step diagrams on how to accomplish this. You could even use it as a generator straight out of the hard drive but it will not supply that much current or voltage. You will be able to light a few LED's without any modifications but that is about it.

For those that say that you can not reuse a hard drive's brushless (BLDC) motor for anything easily, they are sadly mis-informed or they just do not wish to learn, they do not know or they just want tutorials that explain everything because they can not think for themselves.